Dual energy storage system and starter battery module

ABSTRACT

The present disclosure relates to a dual energy storage system that includes a lithium ion battery electrically coupled in parallel with a lead acid battery, where the lithium ion battery and the lead-acid battery are electrically coupled to a vehicle bus, where the lithium ion battery open circuit voltage (OCV) partially matches the lead-acid battery OCV such that the lead-acid battery OCV at 100% of the lead-acid battery state of charge (SOC) is about equal to the lithium ion battery OCV at 50% of the lithium ion battery SOC.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application under 35 U.S.C. §371 of International Application No. PCT/US17/32878 entitled “12 VOLTDUAL ENERGY STORAGE SYSTEM AND 12 VOLT STARTER BATTERY,” filed on 16 May2017, which claims priority to and the benefit of U.S. ProvisionalApplication Ser. No. 62/337,128, entitled “12 VOLT DUAL ENERGY STORAGESYSTEM AND 12 VOLT STARTER BATTERY,” filed 16 May 2016, both of whichare incorporated by reference herein in their entirety for all purposes.

BACKGROUND

The present disclosure relates generally to the field of batteries andbattery modules. More specifically, the present disclosure relates tolithium ion battery cells that may be used with a dual energy storagesystem and starter battery modules.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described below. This discussion is believed to be helpful inproviding the reader with background information to facilitate a betterunderstanding of the various aspects of the present disclosure.Accordingly, it should be understood that these statements are to beread in this light, and not as admissions of prior art.

A vehicle that uses one or more battery systems for providing all or aportion of the motive power for the vehicle can be referred to as anxEV, where the term “xEV” is defined herein to include all of thefollowing vehicles, or any variations or combinations thereof, that useelectric power for all or a portion of their vehicular motive force. Forexample, xEVs include electric vehicles (EVs) that utilize electricpower for all motive force. As will be appreciated by those skilled inthe art, hybrid electric vehicles (HEVs), also considered xEVs, combinean internal combustion engine propulsion system and a battery-poweredelectric propulsion system, such as 48 Volt (V) or 130V systems. Theterm HEV may include any variation of a hybrid electric vehicle. Forexample, full hybrid systems (FHEVs) may provide motive and otherelectrical power to the vehicle using one or more electric motors, usingonly an internal combustion engine, or using both. In contrast, mildhybrid systems (MHEVs) disable the internal combustion engine when thevehicle is idling and utilize a battery system to continue powering theair conditioning unit, radio, or other electronics, as well as torestart the engine when propulsion is desired. The mild hybrid systemmay also apply some level of power assist, during acceleration forexample, to supplement the internal combustion engine. Mild hybrids aretypically 96V to 130V and recover braking energy through a belt or crankintegrated starter generator. Further, a micro-hybrid electric vehicle(mHEV) also uses a “Stop-Start” system similar to the mild hybrids, butthe micro-hybrid systems of a mHEV may or may not supply power assist tothe internal combustion engine and operate at a voltage below 60V. Forthe purposes of the present discussion, it should be noted that mHEVstypically do not technically use electric power provided directly to thecrankshaft or transmission for any portion of the motive force of thevehicle, but an mHEV may still be considered as an xEV since it does useelectric power to supplement a vehicle's power needs when the vehicle isidling with internal combustion engine disabled and recovers brakingenergy through an integrated starter generator. In addition, a plug-inelectric vehicle (PEV) is any vehicle that can be charged from anexternal source of electricity, such as wall sockets, and the energystored in the rechargeable battery packs drives or contributes to drivethe wheels. PEVs are a subcategory of EVs that include all-electric orbattery electric vehicles (BEVs), plug-in hybrid electric vehicles(PHEVs), and electric vehicle conversions of hybrid electric vehiclesand conventional internal combustion engine vehicles.

xEVs as described above may provide a number of advantages as comparedto more traditional gas-powered vehicles using only internal combustionengines and traditional electrical systems, which are typically 12Vsystems powered by a lead acid battery. For example, xEVs may producefewer undesirable emission products and may exhibit greater fuelefficiency as compared to traditional internal combustion vehicles and,in some cases, such xEVs may eliminate the use of gasoline entirely, asis the case of certain types of EVs or PEVs.

As technology continues to evolve, there is a need to provide improvedpower sources, particularly battery modules, for such vehicles. Forexample, battery modules that include battery cells with relatively highnominal voltages may reduce a size and cost of the battery modulebecause fewer battery cells are included within the battery module.Additionally, it is also desirable for battery modules to be configuredto operate within existing electrical networks of xEVs withoutdisrupting operation of the xEV electrical network.

SUMMARY

A summary of certain embodiments disclosed herein is set forth below. Itshould be understood that these aspects are presented merely to providethe reader with a brief summary of certain embodiments and that theseaspects are not intended to limit the scope of this disclosure. Indeed,this disclosure may encompass a variety of aspects that may not be setforth below.

The present disclosure relates to a dual energy storage system thatincludes a lithium ion battery electrically coupled in parallel with alead acid battery, where the lithium ion battery and the lead-acidbattery are electrically coupled to a vehicle bus, where the lithium ionbattery open circuit voltage (OCV) partially matches the lead-acidbattery OCV such that the lead-acid battery OCV at 100% of the lead-acidbattery state of charge (SOC) is about equal to the lithium ion batteryOCV at 50% of the lithium ion battery SOC.

The present disclosure also relates to a system that includes a lithiumion starter battery, a lead acid battery electrically coupled inparallel with the lithium ion starter battery, and a vehicle having avehicle bus configured to establish an electrical pathway between thelithium ion starter battery, the lead acid battery, and the vehicle, andwhere the lithium ion starter battery open circuit voltage (OCV)partially matches the lead-acid battery OCV such that the lead-acidstarter battery OCV at 100% of the lead-acid battery state of charge(SOC) is about equal to the lithium ion starter battery OCV at 50% ofthe lithium ion starter battery SOC.

The present disclosure also relates to a method that includes measuringa voltage of a lithium ion battery cell using a voltage sensor,estimating a state of charge (SOC) of the lithium ion battery cell basedon the voltage of the lithium ion battery cell and a voltage profile ofthe lithium ion battery cell, and determining a diagnostic parameter ofthe lithium ion battery cell based on the SOC of the lithium ion batterycell, the voltage of the lithium ion battery cell, or both.

DRAWINGS

Various aspects of this disclosure may be better understood upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 is a perspective view of a vehicle having a battery systemconfigured in accordance with present embodiments to provide power forvarious components of the vehicle, in accordance with an aspect of thepresent disclosure;

FIG. 2 is a cutaway schematic view of an embodiment of the vehicle andthe battery system of FIG. 1, in accordance with an aspect of thepresent disclosure;

FIG. 3 is an embodiment of a chart illustrating a voltage profile for alead acid battery module and a lithium ion battery module, in accordancewith an aspect of the present disclosure;

FIG. 4 is an embodiment of a chart illustrating example voltage profilesfor individual lithium ion battery cells of the lithium ion batterymodule when the lithium ion battery module includes four lithium ionbattery cells or five lithium ion battery cells, in accordance with anaspect of the present disclosure;

FIG. 5 is a perspective view of an embodiment of the lithium ion batterymodule having four lithium ion battery cells, in accordance with anaspect of the present disclosure;

FIG. 6 is a perspective view of an embodiment of the lithium ion batterymodule having four lithium ion battery cells arranged in a two by twoarrangement, in accordance with an aspect of the present disclosure;

FIG. 7 is a perspective view of an embodiment of the lithium ion batterymodule having five lithium ion battery cells, in accordance with anaspect of the present disclosure;

FIG. 8 is a perspective view of an embodiment of the lithium ion batterymodule having six lithium ion battery cells, in accordance with anaspect of the present disclosure; and

FIG. 9 is a flow chart of an embodiment of a process for determining adiagnostic parameter of a lithium ion battery cell, in accordance withan aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, not all featuresof an actual implementation are described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

The battery systems described herein may be used to provide power tovarious types of electric vehicles (xEVs) and other high voltage energystorage/expending applications (e.g., electrical grid power storagesystems). Such battery systems may include one or more battery modules,each battery module having a number of battery cells (e.g., lithium-ion(Li-ion) electrochemical cells) arranged and electrically interconnectedto provide particular voltages and/or currents useful to power, forexample, one or more components of an xEV. As another example, batterymodules in accordance with present embodiments may be incorporated withor provide power to stationary power systems (e.g., non-automotivesystems).

xEvs may include a lead acid battery module (e.g., having an opencircuit voltage of 12V at 100% state of charge) and a Li-ion batterymodule (e.g., having an open circuit voltage of between 12.5V and 16V at100% state of charge) coupled to one another in a parallelconfiguration. In certain instances, the lead acid battery module may beused to start and/or ignite an internal combustion engine of the xEV,whereas the Li-ion battery module may be used to capture power from aregenerative braking system and to provide electricity to vehiclecomponents when the internal combustion engine is idle. Additionally oralternatively, the Li-ion battery module may be utilized as a starterbattery and provide power to start and/or ignite an internal combustionengine of the xEV. Accordingly, Li-ion batteries in 12V vehiclearchitectures can apply to 12V Dual Energy Storage Systems (DESS) and12V starter applications. Unfortunately, to supply a sufficient amountof power, Li-ion battery modules include a plurality of individualLi-ion battery cells, which may add weight to the xEV and/or decreasefuel economy.

The present disclosure addresses these and other shortcomings oftraditional Li-ion battery modules. For example, embodiments of thepresent disclosure relate to high voltage Li-ion battery cells that mayform a Li-ion battery module configured to be utilized in existingelectrical networks of an xEV without disrupting the xEV electricalnetwork (e.g., the battery module provides power within a predeterminedrange). The high voltage Li-ion battery cells may reduce a size (e.g.,volume) of the overall battery module by reducing a number of Li-ionbattery cells that are included in the battery module. Further, the highvoltage Li-ion battery cells may reduce costs of the battery modulebecause of the reduced number of the Li-ion battery cells.

In some embodiments, the Li-ion battery module is configured to have anopen circuit voltage (OCV) at 50% state of charge (SOC) that issubstantially equal to (e.g., within 10% of, within 5% of, or within 1%of) the OCV of the lead acid battery module at 100% SOC of the lead acidbattery module. Thus, the Li-ion battery module may be configured toreceive charge (e.g., via regenerative braking system) while the leadacid battery is configured to provide power (e.g., to the ignitionsystem or other electrical components of the xEV during rapid dischargeconditions). Further, each Li-ion battery cell of the Li-ion batterymodule may have a particular chemical configuration that enables avoltage profile of the Li-ion battery cell to have an increased slope(e.g., a voltage profile having a steeper incline). Increasing the slopeof the voltage profile enables an accurate estimation of SOC of anindividual Li-ion battery cell based on a measured voltage of theindividual Li-ion battery cell. The estimated SOC and/or the measuredvoltage enables a diagnostic parameter and/or status of the individualLi-ion battery cell (or, in some cases, the overall battery module) tobe determined.

To help illustrate the manner in which the present embodiments may beused in a system, FIG. 1 is a perspective view of an embodiment of avehicle 10 (e.g., an xEV), which may utilize a regenerative brakingsystem. Although the following discussion is presented in relation tovehicles with regenerative braking systems, the techniques describedherein are adaptable to other vehicles that capture/store electricalenergy with a battery, which may include electric-powered andgas-powered vehicles. Further, embodiments may be employed in stationarypower systems as well.

As discussed above, it would be desirable for a battery system 12 to belargely compatible with traditional vehicle designs. Accordingly, thebattery system 12 may be placed in a location in the vehicle 10 thatwould have housed a traditional battery system. For example, asillustrated, the vehicle 10 may include the battery system 12 positionedsimilarly to a lead-acid battery of a typical combustion-engine vehicle(e.g., under the hood of the vehicle 10).

A more detailed view of the battery system 12 is described in FIG. 2. Asdepicted, the battery system 12 includes an energy storage component 13coupled to an ignition system 14, an alternator 15, a vehicle console16, and optionally to an electric motor 17. Generally, the energystorage component 13 may capture/store electrical energy generated inthe vehicle 10 and output electrical energy to power electrical devicesin the vehicle 10.

In other words, the battery system 12 may supply power to components ofthe vehicle's electrical system, which may include radiator coolingfans, climate control systems, electric power steering systems, activesuspension systems, auto park systems, electric oil pumps, electricsuper/turbochargers, electric water pumps, heated windscreen/defrosters,window lift motors, vanity lights, tire pressure monitoring systems,sunroof motor controls, power seats, alarm systems, infotainmentsystems, navigation features, lane departure warning systems, electricparking brakes, external lights, or any combination thereof.Illustratively, in the depicted embodiment, the energy storage component13 supplies power to the vehicle console 16 and the ignition system 14,which may be used to start (e.g., crank) an internal combustion engine18.

Additionally, the energy storage component 13 may capture electricalenergy generated by the alternator 15 and/or the electric motor 17. Insome embodiments, the alternator 15 may generate electrical energy whilethe internal combustion engine 18 is running. More specifically, thealternator 15 may convert the mechanical energy produced by the rotationof the internal combustion engine 18 into electrical energy.Additionally or alternatively, when the vehicle 10 includes an electricmotor 17, the electric motor 17 may generate electrical energy byconverting mechanical energy produced by the movement of the vehicle 10(e.g., rotation of the wheels) into electrical energy. Thus, in someembodiments, the energy storage component 13 may capture electricalenergy generated by the alternator 15 and/or the electric motor 17during regenerative braking. As such, the alternator 15 and/or theelectric motor 17 are generally referred to herein as a regenerativebraking system.

To facilitate capturing and supplying electric energy, the energystorage component 13 may be electrically coupled to the vehicle'selectric system via a bus 19. For example, the bus 19 may enable theenergy storage component 13 to receive electrical energy generated bythe alternator 15 and/or the electric motor 17. Additionally, the bus 19may enable the energy storage component 13 to output electrical energyto the ignition system 14 and/or the vehicle console 16. Accordingly,when a 12 volt battery system 12 is used, the bus 19 may carryelectrical power typically between 8-18 volts.

Additionally, as depicted, the energy storage component 13 may includemultiple battery modules. For example, in the depicted embodiment, theenergy storage component 13 includes a Li-ion (e.g., a first) batterymodule 20 in accordance with present embodiments, and a lead-acid (e.g.,a second) battery module 22, where each battery module 20, 22 includesone or more battery cells (e.g., individually sealed battery cells). Inother embodiments, the energy storage component 13 may include anynumber of battery modules. Additionally, although the Li-ion batterymodule 20 and lead-acid battery module 22 are depicted adjacent to oneanother, they may be positioned in different areas around the vehicle.For example, the lead-acid battery module 22 may be positioned in orabout the interior of the vehicle 10 while the Li-ion battery module 20may be positioned under the hood of the vehicle 10.

In some embodiments, the energy storage component 13 may includemultiple battery modules to utilize multiple different batterychemistries. For example, when the Li-ion battery module 20 is used,performance of the battery system 12 may be improved since the Li-ionbattery chemistry generally has a higher coulombic efficiency and/or ahigher power charge acceptance rate (e.g., higher maximum charge currentor charge voltage) than the lead-acid battery chemistry. As such, thecapture, storage, and/or distribution efficiency of the battery system12 may be improved.

To facilitate controlling the capturing and storing of electricalenergy, the battery system 12 may additionally include a control module24. More specifically, the control module 24 may control operations ofcomponents in the battery system 12, such as relays (e.g., switches)within the energy storage component 13, the alternator 15, and/or theelectric motor 17. For example, the control module 24 may regulate anamount of electrical energy captured/supplied by each battery module 20or 22 (e.g., to de-rate and re-rate the battery system 12), perform loadbalancing between the battery modules 20 and 22, determine a state ofcharge (SOC) of each battery module 20 or 22, determine a temperature ofeach battery module 20 or 22, control voltage output by the alternator15 and/or the electric motor 17, and the like.

Accordingly, the control module 24 may include one or more processor 26and one or more memory 28. More specifically, the one or more processor26 may include one or more application specific integrated circuits(ASICs), one or more field programmable gate arrays (FPGAs), one or moregeneral purpose processors, or any combination thereof. Additionally,the one or more memory 28 may include volatile memory, such as randomaccess memory (RAM), and/or non-volatile memory, such as read-onlymemory (ROM), optical drives, hard disc drives, or solid-state drives.In some embodiments, the control module 24 may include portions of avehicle control unit (VCU) and/or a separate battery control module.

As discussed above, Li-ion batteries in 12V vehicle architectures canapply to 12V Dual Energy Storage Systems (DESS) and 12V starterapplications. In a 12V DESS application, the Li-ion battery 20 (e.g., amodule having several Li-ion battery cells) may be connected in parallelto the lead acid (PbA) battery 22, and both may be connected to thevehicle's electrical bus 19. For 12V DESS, it is now recognized that itmay be desirable for the Li-ion battery open circuit voltage (OCV) topartially match the lead acid battery OCV, such that the OCV of the leadacid battery at 100% state of charge (SOC) is about equal to the OCV ofthe Li-ion battery at 50% SOC. An example of this OCV relationship isset forth in FIG. 3.

FIG. 3 is an embodiment of a chart 94 illustrating OCV 96 as a functionof SOC 98 for the lead-acid battery 22 (e.g., represented by line 100)and the Li-ion battery 20 (e.g., represented by line 102). As shown inthe illustrated embodiment of FIG. 3, the 12V Li-ion battery system 20has a voltage profile where at 50% SOC (shown at point 104), the Li-ionbattery system 20 has a voltage of about (e.g., within 10% of, within 5%of, within 1% of) 13V. At 100% SOC, the lead acid battery 22 has avoltage (as shown at point 106) that is about equal to (e.g., within 10%of, within 5% of, within 1% of) the voltage of the Li-ion battery system20 at 50% SOC (as shown at point 104). To the extent that the lead acidbattery 22 and Li-ion battery 20 voltages do not exactly match, it ispresently recognized that the voltage of the Li-ion battery 20 at 50%SOC may be within about 150 milliVolts (mV) or between 1% and 2% of thelead acid battery 22 voltage at 100% SOC.

This OCV/SOC relationship between the lead acid battery 22 and theLi-ion battery 20 may enable the DESS to be balanced in a way thatenables top end regenerative capacity and low end discharge capacity.More specifically, this relationship encourages charge acceptance usingthe Li-ion battery 20 during times of regeneration (e.g., charging), andencourages discharging from the lead acid battery 22 in times whererapid discharge is experienced by the energy storage component 13.

The top end regenerative capacity may generally correspond to theability of the Li-ion battery 20 to accept charge from a regenerativesystem (e.g., a regenerative braking system) even when the lead acidbattery 22 is at 100% SOC. The low end discharge capacity may generallycorrespond to the ability of the lead acid battery 22 to providedischarge current even when the Li-ion battery 20 is at 50% SOC.Additionally or alternatively, the low end discharge capacity maycorrespond to the ability of the Li-ion battery 20 to provide dischargecurrent when the lead acid battery 22 is at its lowest desired operatingSOC (e.g., 80% SOC). For example, the Li-ion battery 20 may have an SOCgreater than 10% at a voltage where the lead acid battery 22 is at 80%SOC. In the illustrated embodiment of FIG. 3, the lead acid battery 22has a voltage of about 12.6V at 80% SOC (as shown at point 108), and theLi-ion battery 20 has an SOC of about (e.g., within 10% of, within 5%,or within 1% of) 20% at 12.6V (as shown at point 110).

As discussed above, it is also now recognized that it may be desirablefor the voltage profile of the Li-ion battery 20 to have some degree ofcurvature within its expected SOC operating range. For example, certaindiagnostic measurements relating to the Li-ion battery 20 may beperformed based on voltage measurements and associated SOC estimates todetermine diagnostic parameters, such as a health of the Li-ion battery20 and/or a remaining operating life of the Li-ion battery 20. Morespecifically, the voltage of the Li-ion battery 20 may be measured(e.g., via a voltage sensor), and the SOC of the Li-ion battery 20 maybe estimated based on the Li-ion battery voltage measurements. If thevoltage remains relatively flat across a wide SOC range (i.e., theprofile has little to no curvature or a very small slope), then smallchanges in the voltage measurement may cause relatively large changes inSOC estimation. Thus, it may be desirable to design the Li-ion battery20 to have a voltage profile with a slope that is sufficiently largerthan the degree of voltage measurement uncertainty, which may enablerobust SOC estimation.

Such a Li-ion battery 20 could be developed using 4, 5, or 6 Li-ionbattery cells (see, e.g., FIGS. 5-8). However, the system costs, systemfootprint, system cooling requirements, and similar considerationsrelating to the Li-ion battery module, may be directly related to thenumber of battery cells in the system. To reduce total system costs,either alone or in combination with reducing system footprint andcooling requirements, it may be desirable to have the minimum number ofbattery cells in the system that provides the voltage matching describedabove. For a 4-cell system, a Li-ion battery cell with a nominal voltageof about 3.25V may be appropriate. For a 5-cell system, a Li-ion batterycell with a nominal voltage of about 2.6V may be appropriate. SuchLi-ion battery cells could also be used to produce a 12V starterbattery. The battery-level voltage could be compliant to existingvehicle voltage architectures, and would also benefit total system costreduction by minimizing the total cell count. In accordance with presentembodiments, each of the Li-ion battery cells may combine to produce anominal battery module voltage of between 12V and 16V, between 12.5V and15.5V, or between 13V and 15V. Further, in some embodiments, the Li-ionbattery module 20 may have a voltage between 12.5 and 13.5V, between12.8V and 13.4V, or between 13V and 13.2V at 50% SOC. As such, theLi-ion battery module 20 may be configured to operate within theelectrical bus 19 of the vehicle 10 without disrupting the bus 19 (e.g.,the bus 19, or components associated with the bus 19, may be sensitiveat voltages above 15.5V and below 12.5V) and/or the control module 24.For example, in some cases a battery module that operates with a voltagethat is above a high voltage threshold (e.g., 15.5V or 16V) or below alow voltage threshold (e.g., 11V or 12.5V) may interfere with thecontrol module 24 and/or other electronic components associated with thebus 19. Therefore, the Li-ion battery module 20 of the presentdisclosure may reduce and/or eliminate interference with the controlmodule 24 and/or the bus 19.

FIG. 4 is an embodiment of a chart 138 illustrating battery voltage 140(e.g., OCV) as a function of SOC 142 for each Li-ion battery cell of a4-cell Li-ion battery module (represented by line 144) and a 5-cellLi-ion battery module (represented by line 146). For the 4-cellarchitecture, as shown by line 144, each Li-ion battery cell has ahigher nominal voltage when compared to the 5-cell architecture.Further, at 50% SOC, each of the Li-ion battery cells of the 4-cellarchitecture has an OCV of about 3.26 V. For a 5-cell architecture, eachLi-ion battery cell has a slightly lower nominal voltage as compared tothe 4-cell architecture, and has an OCV of about 2.6 V at 50% SOC.

As discussed above, an increased slope of the voltage profile for theLi-ion battery cells may facilitate an estimation of SOC based on avoltage measurement of the Li-ion battery cell. As shown in theillustrated embodiment of FIG. 4, linear trend lines were calculated tofit the actual voltage profiles for both the Li-ion battery cells of the4-cell Li-ion battery module (as shown by line 148) and the 5-cellLi-ion battery module (as shown by line 150). The linear trend lineseach include a slope that characterizes a change in voltage of theLi-ion battery cell as a function of change in SOC of the Li-ion batterycell. The slope of the linear trend lines of FIG. 4 is referred toherein as an average slope of the voltage profiles of the Li-ion batterycells. The linear trend line of the Li-ion battery cell of the 4-cellLi-ion battery module 20 includes an average slope of approximately(e.g., within 10% of, within 5% of, or within 1% of) 0.0056 Volts/SOC(%). The linear trend line of the Li-ion battery cell of the 5-cellLi-ion battery module 20 includes an average slope of approximately0.0045 Volts/SOC (%). Accordingly, in some embodiments, the Li-ionbattery cells may include a voltage profile having an average slope ofbetween 0.0010 Volts/SOC (%) and 0.010 Volts/SOC (%), between 0.0020Volts/SOC (%) and 0.0080 Volts/SOC (%), or between 0.0040 Volts/SOC (%)and 0.0060 Volts/SOC (%). While the trend lines in the illustratedembodiment of FIG. 4 are linear, it should be recognized that othersuitably shaped trend lines may be calculated to determine a slope ofthe voltage profiles (a change in voltage as a function of SOC) for theLi-ion battery cells and/or to estimate the SOC of the Li-ion batterycells.

FIG. 5 is a perspective schematic view of an embodiment of the Li-ionbattery module 20 having four Li-ion battery cells 160 in a four by onearrangement. As shown in the illustrated embodiment of FIG. 5, each ofthe four Li-ion battery cells 160 are disposed in a battery modulehousing 162. Further, the four Li-ion battery cells 160 may be coupledto one another via bus bars 164 disposed over battery cell terminals166. In some embodiments, each of the four Li-ion battery cells 160 arecoupled to one another in series to form the Li-ion battery module 20having a voltage of 12V. As such, the bus bars 164 may connect apositive terminal of a Li-ion battery cell 160 to a negative terminal ofan adjacent Li-ion battery cell 160 to couple the Li-ion battery cells160 in series. However, in other embodiments, the Li-ion battery cells160 may be coupled to one another in another suitable configuration toform the Li-ion battery module 20 having a voltage 12V.

Further, a lid 168 having module terminals 170 may be disposed over anopening 172 of the housing 162. The module terminals 170 may be coupledto battery cell terminals 166 at respective ends 174 and 176 of thebattery module housing 160 in order to establish an electricalconnection between the Li-ion battery cells 160 and the module terminals170. Accordingly, the module terminals 170 may be coupled to theelectrical bus 19 and/or another suitable device to provide power fromthe Li-ion battery cells 160 to a load.

FIG. 6 is a perspective schematic view of an embodiment of the Li-ionbattery module 20 having four of the Li-ion battery cells 160 in a twoby two arrangement. As shown in the illustrated embodiment of FIG. 6,the Li-ion battery cells 160 are still coupled to one another in series,such that the bus bars 164 couple a positive terminal of a Li-ionbattery cell 160 to a negative terminal of an adjacent Li-ion batterycell 160 (e.g., either directly adjacent or diagonally adjacent). Whilethe bus bars 164 are shown in a diagonal configuration between thebattery cell terminals 166, it should be recognized that other batterycell terminal 166 and bus bar 164 configurations may be utilized.

FIGS. 7 and 8 are perspective schematic views of embodiments of theLi-ion battery module 20 having five of the Li-ion battery cells 160 andsix of the Li-ion battery cells 160, respectively. Again, the Li-ionbattery cells 160 may be coupled to one another in a seriesconfiguration and/or another suitable configuration to form the Li-ionbattery module 20 having a voltage of 12V.

The amount of the Li-ion battery cells 160 included in the batterymodule 20 (e.g., 4, 5, 6, or another suitable amount) may be dependenton a chemical configuration of the Li-ion battery cells 160, whichproduces a predetermined nominal voltage (e.g., 2.6V or 3.26V).Generally, Li-ion battery cells will include a cathode (a positiveelectrode), an anode (a negative electrode), and an electrolyte. Thecathode and anode each include an electrode active material that enablesthe electrodes to store and transfer ions (e.g., Li-ions) duringcharging and discharging cycles. Whether the electrode active materialis suitable for the cathode or the anode is generally determined by thereference voltage of the electrode active material versus Li⁺/Li⁰. Thenegative electrode active materials of the Li-ion battery cells may beconsidered to include electrode active materials having a voltage thatis lower versus Li⁺/Li⁰ compared to the positive electrode activematerials. The nominal voltages set forth above may be achievedprimarily through appropriate selection and combination of activematerial chemistries for the cathode as well as the use of a suitableanode active material, although electrolyte chemistry may also have aneffect on cell operation. For instance, the nominal voltage of theLi-ion battery cells may be the voltage of the positive electrode activematerial versus Li⁺/Li⁰, less the voltage of the negative electrodeactive material versus Li⁺/Li⁰.

The electrode active materials may generally be of any type,configuration, or chemistry, as long as the combination of cathodeactive materials and anode active materials provide the nominal voltagesand voltage profiles set forth above. As an example, the anode activematerial may include graphite or may include a titanate-based material(e.g., lithium titanate, LTO). The cathode active material may includeany one or a combination of different lithiated metal oxides, mixedmetal oxide components, or lithium metal phosphates.

As used herein, lithiated metal oxides and mixed metal oxide componentsfor the cathode active material may refer to any class of materialswhose formula includes lithium and oxygen as well as one or moreadditional metal species (e.g., nickel, cobalt, manganese, aluminum,iron, or another suitable metal). A non-limiting list of examplelithiated metal oxides may include: mixed metal compositions includinglithium, nickel, manganese, and cobalt ions such as lithium nickelcobalt manganese oxide (NMC, LiNi_(x)Mn_(y)Co_(z)O₂, where x+y+z=1),lithium nickel cobalt aluminum oxide (NCA) (e.g.,LiNi_(x)Co_(y)Al_(z)O₂, where x+y+z=1), lithium cobalt oxide (LCO)(e.g., LiCoO₂), and lithium manganese oxide spinel (LMO-spinel) (e.g.,LiMn₂O₄).

Layered-layered material and/or layered-layered spinel material may alsobe utilized as a cathode active material. Layered-layered materials mayhave the formula: xLi₂M¹O₃⋅(1−x)LiM²O₂, wherein: M¹ is Mn, Ti, Zr, andcombinations thereof; M² is Mn, Ni, Co, Cr, and combinations thereof,and x is greater than 0 and smaller than 1. As a further example,layered-layered materials may include xLi₂MnO₃⋅(1−x)LiMO₂ (M=Mn, Ni),and may have relatively high reference voltages (>4.4 V vs. Li⁺/Li⁰).Layered-layered spinel materials have a similar structure, and alsoinclude an embedded spinel component. A spinel structure may refer to achemical substance that has a cubic, close-packed lattice configuration.Such layered-layered spinel materials may be produced by reducing theoverall lithium content of a parent layered-layered material, whilemaintaining the Mn:M ratio at a constant value. One example of alayered-layered spinel may be represented by the formulaLi_(x)Mn_(0.65)Ni_(0.35)O_(y), for which the end members are0.3Li₂MnO₃⋅0.7LiMn_(0.5)Ni_(0.5)O₂ (x=1.3; y=2.3), in which the averagemanganese and nickel oxidation states are 4+ and 2+, respectively, andLiMn_(1.3)Ni_(0.7)O₄ (x=0.5; y=2) in which the corresponding averageoxidation states are expected to lie between 4+ and 3.77+ for Mn, and2.57+ and 3+ for Ni, respectively. Certain layered-layered spinelcathode materials may have voltages higher than 4.4 V vs. Li⁺/Li⁰, suchas up to about 5 V vs. Li⁺/Li⁰.

Such materials may be considered high voltage spinel (HVS) activematerials, and may be referenced using spinel notation. HVS materialsmay have a chemical formula of LiM_(x)Mn_(2-x)O₄ (using conventionalspinel notation), where x may be between 0.35 and 0.65 and M representsa metal, such as a transition metal. As an example, the metal (M) may benickel, chromium, iron, or another transition metal. In certainembodiments, HVS may have the chemical formula LiMn_(1.5)Ni_(0.5)O₄, orLiNi_(0.4)Mn_(1.6)O₄, or LiNiMnO₄, for example. Further, suchembodiments of HVS may be metal doped on the nickel side (e.g., toreplace a portion of the Ni with another metal) or metal doped on themanganese side (e.g., to replace a portion of the Mn with anothermetal). In certain embodiments, HVS has a nominal voltage of about 4.4 Vversus Li⁺/Li⁰, although higher voltages may be achieved throughappropriate selection of constituent layers (e.g., in a layered-layeredmaterial).

Lithium metal phosphates for the cathode active material may refer tomaterials whose formula includes lithium and phosphate as well as one ormore additional metal species (e.g., nickel, cobalt, manganese, iron, oranother suitable metal). For example, such lithium metal phosphates maybe represented as LiMPO₄, wherein M is Mn, Co, Ni, Fe, Zn, Cu, Ti, Sn,Zr, V, Al, and mixtures thereof. A non-limiting list of example lithiummetal phosphates may include: lithium nickel phosphate (LiNiPO₄),lithium cobalt phosphate (LiCoPO₄), lithium nickel manganese phosphate(LiNiMnPO₄), lithium iron phosphate (LiFePO₄), and lithium manganeseiron phosphate (LiMnFePO₄).

Again, the cathode active materials may be used alone or in anappropriate combination to achieve a suitable nominal voltage andvoltage profile. Each combination may provide a particular nominalvoltage and a particular voltage profile. As an example, a first cathodeactive material may be combined (e.g., physically blended) with one ormore second cathode active materials, and the blended combination may becoated onto an appropriate collector to produce a cathode. Accordingly,each Li-ion battery cell may include a cathode having one, two, three ormore active materials. Thus, the Li-ion battery cells described hereinmay each have a cathode formed using any one or a combination of activematerials selected from a group including or, alternatively, consistingof: LiNi_(x)Mn_(y)Co_(z)O₂, where x+y+z=1; LiNi_(x)Co_(y)Al_(z)O₂, wherex+y+z=1; LiCoO₂; LiMn₂O₄; LiM_(x)Mn_(2-x)O₄; where x may be between 0.35and 0.65 and M is nickel, chromium, or iron; LiMPO₄, wherein M is Mn,Co, Ni, Fe, Zn, Cu, Ti, Sn, Zr, V, Al, and mixtures thereof such asLiNiPO₄; LiCoPO₄; LiNiMnPO₄; LiFePO₄; and LiMnFePO₄.

In accordance with certain embodiments of the present disclosure, thenegative electrode active materials may include certain titanate species(e.g., LTO), graphite, or a combination of the two. In still furtherembodiments, the negative electrode active material may include otherelectrode active materials either alone or in combination with LTOand/or graphite. Additionally, in certain embodiments LTO may have aspinel structure. As a non-limiting example, LTO may have a chemicalformula of Li₄Ti₅O₁₂. LTO may be cation doped and/or anion doped viametal doping or electronegative atom doping, respectively. One exampleis metal fluorine doping. Doping may change the chemical formula of LTOto M-Li₄Ti₅O₁₂, where M represents a metal, such as a transition metal.As an example, the metal (M) may be barium, strontium, molybdenum,neodymium, nickel, manganese, chromium, tungsten, lanthanum, or anothertransition metal. Additionally, or alternatively, LTO may be carboncoated such that the LTO used to produce the negative electrode mayinclude between 0.05% and 1% by weight carbon nanotubes or carbonnanofibers. The carbon coating may enhance conductivity of the LTO, andmay passivate the LTO (e.g., via a passive layer) to suppress gasgeneration from a reaction with electrolyte. To form carbon coated LTO,a mechanical mixing process, such as milling, may be used. In certainembodiments, LTO may have a voltage of about 1.55V versus Li⁺/Li⁰.

In view of the foregoing, it should be appreciated that a number ofdifferent chemistries may be utilized in accordance with the nominalvoltage and voltage profile considerations described herein. It ispresently contemplated that battery cells having the nominal voltage andvoltage profiles described herein may be produced using appropriateselection of one or a combination of the lithium metal oxide, lithiummetal phosphate, high voltage spinel, or layered-layered cathodematerials described above.

For a 4-cell system having the desired voltage profile, and in whicheach cell has a nominal voltage of about 3.26 V, it is presentlycontemplated that such battery cells may be produced using specificcathode and anode active materials. For instance and by way ofnon-limiting example, higher voltage cathode materials such as HVS,either alone or in combination with one or more lithium metal oxides(e.g., NMC, NCA) may be utilized. In such embodiments, LTO may be usedas the anode active material. When graphite is used as the anode activematerial, such high voltage cathode active materials may not necessarilybe required, but may be used where deemed beneficial. For a 5-cellsystem in which each cell has a nominal voltage of about 2.6 V, a widevariety of cathode and anode active materials may be chosen.

FIG. 9 is a flow chart of an embodiment of a process 200 that isutilized to determine a diagnostic parameter and/or status of a Li-ionbattery cell 160 (e.g., a health of the Li-ion battery cell 160, anoperating life of the Li-ion battery cell 160, a remaining charge of theLi-ion battery cell 160, among others). For example, at block 202, avoltage of the Li-ion battery cell 160 is measured using a voltagesensor disposed in the housing 162 of the Li-ion battery module 20. Insome embodiments, the voltage measurement of the Li-ion battery cell 160may be directed to the control module 24 as feedback. The control module24 may store the voltage profile of the Li-ion battery cell 160 in thememory 28 and estimate the SOC of the Li-ion battery cell 160 based onthe measured voltage, as shown at block 204.

Further, the control module 24 may utilize the SOC and/or the voltagemeasurement of the Li-ion battery cell 160 to determine a diagnosticparameter and/or status of the Li-ion battery cell 160, as shown atblock 206. For example, the control module 24 may utilize the SOC and/orthe voltage of the Li-ion battery cell 160 to calculate and/or estimatea health of the Li-ion battery cell 160, an operating life of the Li-ionbattery cell 160, a remaining charge of the Li-ion battery cell 160, acapacity of the Li-ion battery cell 160, a resistance of the Li-ionbattery cell 160, a current of the Li-ion battery cell 160, atemperature of the Li-ion battery cell 160, degradation of the anodeand/or the cathode of the Li-ion battery cell 160, or a combinationthereof.

One or more of the disclosed embodiments, alone or in combination, mayprovide one or more technical effects useful in the manufacture ofbattery modules, and portions of battery modules. In general,embodiments of the present disclosure include an improved Li-ion batterymodule that includes a voltage at 50% SOC that is substantially equal to(e.g., within 10% of, within 5% of, or within 1% of) a voltage of a leadacid battery module at 100% SOC. As such, the Li-ion battery module mayregenerate (e.g., receive electrical power) even when the lead acidbattery is at full SOC, and the lead acid battery may supply power(e.g., to an xEV) when the Li-ion battery module is at less than 100%SOC. Further, each Li-ion battery cell of the Li-ion battery module mayinclude a voltage profile having an increased slope to facilitate adetermination of a diagnostic parameter and/or status of the Li-ionbattery cell. Further, the Li-ion battery cells may include a chemicalconfiguration that enables the Li-ion battery cells to produce arelatively high voltage. Accordingly, a number of the Li-ion batterycells may be reduced, thereby reducing a size and/or a cost of theLi-ion battery module. The technical effects and technical problems inthe specification are exemplary and are not limiting. It should be notedthat the embodiments described in the specification may have othertechnical effects and can solve other technical problems.

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

1. A dual energy storage system, comprising: a lithium ion batteryconfigured to be electrically coupled in parallel with a lead acidbattery, wherein the lithium ion battery and the lead-acid battery areconfigured to be electrically coupled to a vehicle bus; and wherein thelithium ion battery open circuit voltage (OCV) partially matches thelead-acid battery OCV such that the lead-acid battery OCV at 100% of thelead-acid battery state of charge (SOC) and the lithium ion battery OCVat 50% of the lithium ion battery SOC is approximately 12.9V.
 2. Thedual energy storage system of claim 1, wherein the lithium ion batteryhas a voltage profile with a slope that is sufficiently larger than adegree of voltage measurement uncertainty associated with measurementelectronics of the lithium ion battery to thereby enable robust SOCestimation of the lithium ion battery SOC.
 3. The dual energy storagesystem of claim 1, wherein the lithium ion battery has five lithium ionbattery cells each having a nominal voltage of about 3.26V.
 4. The dualenergy storage system of claim 1, wherein the lithium ion battery hasfour lithium ion battery cells each having a nominal voltage of about2.6V.
 5. The dual energy storage system of claim 1, wherein the lithiumion battery has a plurality of lithium ion battery cells, wherein eachlithium ion battery cell of the plurality of lithium ion battery cellshas a cathode formed from one or more cathode active materials selectedfrom the group consisting of: LiNi_(x)Mn_(y)Co_(z)O₂, where x+y+z=1;LiNi_(x)Co_(y)Al_(z)O₂, where x+y+z=1; LiCoO₂; LiMn₂O₄; LiNiMnO₄,LiM_(x)Mn_(2-x)O₄; where x may be between 0.35 and 0.65 and M is nickel,chromium, or iron; LiMPO₄, wherein M is Mn, Co, Ni, Fe, Zn, Cu, Ti, Sn,Zr, V, Al, and mixtures thereof (such as LiNiPO₄; LiCoPO₄; LiNiMnPO₄;LiFePO₄; and LiMnFePO₄).
 6. The dual energy storage system of claim 1,wherein the plurality of lithium ion battery cells form a total voltageof between 12.5 V and 16.0 V.
 7. The dual energy storage system of claim1, wherein the lithium ion battery and the lead-acid battery areelectrically coupled to the vehicle bus.
 8. The dual energy storagesystem of claim 1, wherein the lithium ion battery has five lithium ionbattery cells.
 9. The dual energy storage system of claim 8, whereineach of the five lithium ion battery cells has a voltage profile with anaverage slope of approximately 0.0045 V/SOC (%)
 10. The dual energystorage system of claim 1, wherein the lithium ion battery has fourlithium ion battery cells.
 11. The dual energy storage system of claim10, wherein each of the four lithium ion battery cells has a voltageprofile with an average slope of approximately 0.0056 V/SOC (%)
 12. Thedual energy storage system of claim 1, wherein the lithium ion batteryhas six lithium ion battery cells.
 13. A system, comprising: a lithiumion battery; a lead acid battery electrically coupled in parallel withthe lithium ion battery; and a vehicle comprising a vehicle busestablishing an electrical pathway between the lithium ion battery, thelead acid battery, and the vehicle; and wherein the lithium ion batteryopen circuit voltage (OCV) partially matches the lead-acid battery OCVsuch that the lead-acid battery OCV at 100% of the lead-acid batterystate of charge (SOC) and the lithium ion battery OCV at 50% of thelithium ion battery SOC is approximately 12.9V.
 14. The system of claim13, wherein the lithium ion battery cell has a lithium ion battery cellwith a nominal voltage of about 2.6 V or a nominal voltage of about 3.26V.
 15. The system of claim 13, wherein the lithium ion battery has fivelithium ion battery cells each having a voltage profile with an averageslope of approximately 0.0045 V/SOC (%).
 16. The system of claim 13,wherein the lithium ion battery has four lithium ion battery cells eachhaving a voltage profile with an average slope of approximately 0.0056V/SOC (%).
 17. A method, comprising: measuring a voltage of a lithiumion battery cell using a voltage sensor; estimating a state of charge(SOC) of the lithium ion battery cell based on the voltage of thelithium ion battery cell and a voltage profile of the lithium ionbattery cell, wherein the voltage profile of the lithium ion batterycell comprises a slope that is sufficiently larger than a degree ofvoltage measurement uncertainty associated with measurement electronicsof the lithium ion battery; and determining a diagnostic parameter ofthe lithium ion battery cell based on the SOC of the lithium ion batterycell, the voltage of the lithium ion battery cell, or both.
 18. Themethod of claim 17, wherein the lithium ion battery cell is part of adual energy storage system of a vehicle or a cell of a lithium ionstarter battery.
 19. The method of claim 17, wherein the voltage profileof the lithium ion battery has an average slope between 0.0040 V/SOC (%)and 0.0060 V/SOC (%).
 20. The method of claim 17, wherein the lithiumion battery cell has a nominal voltage of about 2.6 V or a nominalvoltage of about 3.26 V.